Conventionally, there is known a three-phase synchronous motor which includes a rotor having a plurality of magnetic poles and a stator coil arranged radially inside the rotor (see, for example, Patent Document 1).
In the three-phase synchronous motor, there are arranged three magnetic sensors on one axial side of the stator coil. Between a plurality of permanent magnets and the three magnetic sensors, there are provided three magnetic guide members that guide magnetic flux, which emanates from the plurality of magnetic poles of the rotor, respectively to the three magnetic sensors. Hence, to detect the rotational speed and rotational direction of the rotor, each of the three magnetic sensors detects the magnetic flux guided by a corresponding one of the three magnetic guide members.
Moreover, in a general three-phase synchronous motor, to rotate the rotor, there are employed an inverter circuit and a control circuit which are not described in Patent Document 1. To rotate the rotor, the inverter circuit outputs three-phase alternating current to the stator coil, thereby causing the stator coil to create a rotating magnetic field.
The control circuit detects the position of the rotor based on detection signals of the three magnetic sensors. Then, based on the detected position, the control circuit controls the inverter circuit, causing the three-phase alternating current to be outputted from the inverter circuit to the stator coil. Consequently, based on the three-phase alternating current, the stator coil provides the rotating magnetic field to the plurality of magnetic poles of the rotor. As a result, the rotor rotates in sync with the rotating magnetic field.
Here, the three magnetic sensors are mounted on a circuit board. The circuit board is arranged on the one axial side of the stator coil. The three magnetic sensors and the three magnetic guide members are arranged within a region (angular range) of 120 degrees in mechanical angle. Consequently, it is possible to arrange the three magnetic sensors within a small region.